Just an update on this "tandem speakers" set-up.
With particular thanks to Hifitime, I have carried out a change based on his thoughtful recommendation that Bi-amping would be the better and safer (less potentially damaging) way to achieve good results utilising two pairs of speakers simultaneously.
I am lucky to have an extra set of main outs on my pre-amp so it was pretty easy to integrate the amp module on my old Pioneer SX980 100 watts per chnl into 4 ohms. I find as Hifitime intimated this method would produce better sound and indeed it does. The stage is more natural and wide extending well beyond the speakers, everything seems to breath better and feel very relaxed. I should mention that I did not run my second pair of speakers through the hi-pass on my Janis cross-over amps, I took the full signal out of the Preamp directly to the Pioneer and of course connected the speakers with a new run of good speaker cable. In doing it this way I found that the bass response together with the pair of Janis subs in the room was too exaggerated. I decided to try and tune the rear ports on the Sound Dynamics ti300's bass reflex design speakers by first partially and then fully plugging the ports and that did the trick, it worked well.
I am more than pleased with how this whole thing turned out and I thank all those that weighed in on this subject.
Oh yeah, I almost forgot the annoying "HUMmmmm" is gone, the whole system is once again quiet...
